Information about Boltwoodite

Boltwoodite is a rare uranium silicate mineral that forms as small, bright canary-yellow to pale yellow crystals in the weathered, oxidised zones around uranium ore deposits. It is a collectors’ mineral of scientific as much as aesthetic interest, valued for its vivid colour, its strong fluorescence, and the important geological story told by the element at the heart of its chemistry.

It typically forms as slender, rod-like to needle-like crystals arranged in radiating sprays or wart-like aggregates, usually coating fracture surfaces or cavity walls in the host rock.

Individual crystals rarely exceed a millimetre or two in length, and most boltwoodite specimens are best appreciated under magnification. It is typically canary-yellow to pale yellow or yellowish-green in colour, with a silky to vitreous lustre, and is translucent in thin crystals.

Boltwoodite forms in the outer alteration zone surrounding primary uranium ore minerals such as uraninite as those ores weather near the surface – a natural process in which uranium minerals are broken down and recombined into new secondary species.

It belongs to the uranophane group, and is closely related to natroboltwoodite (the sodium-dominant equivalent) and uranophane itself.

Uses and History

Boltwoodite has no industrial or gemological applications and is collected purely for its scientific interest and its striking fluorescence.

The mineral was first described in 1956 by the American mineralogists Clifford Frondel and Jun Ito, from specimens collected at Pick’s Delta Mine in Emery County, Utah, USA – its type locality. It was named in honour of Professor Bertram Borden Boltwood (1870-1927) of Yale University, one of the founding figures of radiochemistry and the pioneer of uranium-lead (U-Pb) radiometric dating – the method by which the ages of rocks and minerals are measured using the known rate at which uranium decays into lead. Boltwood’s work in the early 20th century was foundational to our modern understanding of geological time, and the naming of a uranium mineral after him is a particularly fitting tribute.

Notable localities for collectable specimens include the Goanikontes uranium prospect in the Erongo Region of Namibia, which has produced the finest crystallised examples known and from which most collectable material on the market originates; the New Method Mine (Hope Uranium Prospect) at Amboy in San Bernardino County, California, where microscopic but well-crystallised sprays occur on calcite matrix; and the Rössing Mine in Namibia, another significant source. Other occurrences are known from Rwanda, Argentina, Australia, and Japan, though most are of scientific rather than collecting interest.

Mineralogy

Hazards and Warnings

Radioactive mineral: contains uranium. Boltwoodite is radioactive and must be handled and stored accordingly. Collectors should wash their hands thoroughly after handling, avoid inhaling any dust, and never place specimens near the mouth. Specimens should ideally be stored away from areas of prolonged human occupation – a sealed display case in a well-ventilated room, kept at some distance from where people spend extended time, is recommended. Specimens should be kept completely out of reach of children.

The radiation level of individual specimens varies and depends on the size and uranium content of the material. For general guidance on the safe handling and storage of radioactive minerals, the Geological Curators Group has published freely available advice that collectors may find useful.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Boltwoodite
• https://www.mindat.org/min-716.html
• https://www.handbookofmineralogy.org/pdfs/boltwoodite.pdf
• https://www.geocurator.org/images/resources/advice/radioactive.pdf